Waterproofing leather



Patented July 17, 1928.

UNITED STATES 1,572,435 ATE-NT r ce.

HENRY V. DUNHAM, OF BAINBRIDGE, NEW YORK, ASSIGNOR J30v TASSEL PANY, OF BOSTON, MASSACHUSETTS, A CORPORATION OF MASSACHUSETTS.

. WATERPROOFING LEATHER.

No Drawing. Application filed July 6,

The present invention relates to the waterproofing of leather and has special reference to waterproofing sole leather or belt leather and other relatively heavy leather but is also applicable to thin leather, split leather, etc. The proces has given particularly favorable results in the waterproofing of chrome leather, under which expression is intended to be included, leather tanned or tawed by means of chromium compOunds either used alone or in conjunction with vegetable tanning materials. As a special example of this, chrome-tanned bark-retanned leather, when treated in accordance with the present invention gives especially favorable re-- sults, notably for shoe soles.- All chrome tanned leather is particularly good as regards wearing properties, for sole leather and the like. However, it is too stifl for many purposes. It also has the objectionable property of absorbing a large amount of water and when in a wet condition it stretches badly and is very slippery. These disadvantages are overcome by my process as described below in which the leather, besides being made waterproof, becomes pliable and non-slippery and the undesired properties above noted are eliminated.

In accordance with the present invention I impregnate leather, particularly of the kind above referred to, with a mixture consisting of a low-viscosity solution of rubber in a wax, say parafiin wax, to which may be added other substances, which are normally solid or semi-solid such as greases, other gums and resins, drying oils in small amount, dyes, etc. However, it is not desirable to employ volatile solvents in the impregnation. Volatile solvents have heretofore been ex- 40 tensively used in the impregnation of leather and other materials with mixtures including parafiin wax, gums or the like, but the use of these solvents is open to serious objection on account of their infiammability and consequent fire risk. Moreover the volatile solvent absorbed during the impregnation subsequently evaporates, with the result that the materials dissolved therein are largely drawn to the surface of the leather vleaving only a very small amount of the impregnating agent in the interior of the leather. Thus the treated leather of such old processes is not sufficiently filled with the rubber and wax and other substances, to possess the desired waterproof qualities.

1926. Serial No. 120,877.

In accordance with the present invention I preferably use a mixture composed largely or entirely of paraffin .waxjand rubber. The paraliin 1s first heated to a temperature substantially above the melting point of the parafi'in, and at well above the softening point of rubber, say 150 (3;, and the rubber, preferably in comminuted form,'is then gradually added to the hot material preferably with stirring while preferably at about 150 C, or a little higher. Obviously 'tem- 1 connection therewith I can also add other 'gums or resins, such as gums thus, gum

sandarac, gum yucca, common rosin or the cumarone resins, and also other'waxes, such as japan wax, Montan wax, etc. I can als employ with the paraffin and rubber, with or without the other ingredients above referred to, non-volatile drying oils such aslinseed oil, tung oil, etc. The materials mentioned in the last two sentences are all organic materials capable of blending with the mixture of rubber and parafiin wax.

In impregnating the leather, the mixture is melted and maintained at a temperature of 90 to 100 C. (preferably 95 to 98 C.) at which temperature the leather is immersed in the molten mixture and allowed to remain for a time depending upon the degree of impregnation desired, the dryness, thick ness, hardness and porosity of the leather and other factors. The pieces of leather can be placed in a vertical or horizontal position in the tank containing the hot molten impregnating materal. The material should be used sufficiently hot to be molten, but temperatures substantially above 100 (3., should generally be avoided as liable to injure the leather. Generally the higher temperatures above given are preferable .as the impregnation is very much more rapid at 95 to 98 0., than say at 75- to 80 C.- At the lower temperatures the impregnating liquid is much more viscous and has less penetrating power. While I do not desire to limit this invention to the use of'these preferred specific temperatures, I call attention to the -fact-that the leather is immersed in a rela- "tively hot mixture, the same being, for instance, hot enough to injure a persons hands if held therein for any substantial time. This invention is thereby sharply difierentiated from greasing boots by applying a soft grease at, or slightly above room temperature.

The impregnating mixture which I .employ most advantageously is, at normal room temperature, a relatively firm solid, usually of a hardness comparable with some of the softer varieties of or stallizable paraflin wax, scale wax, etc., an is not a soft-greasy mass of the consistency of chicken grease goose grease, petroleum etc., commonly used for greasing boots.

I call attention to the fact that the mixture of rubberand paraifin wax is heated preferably to 150 0., or thereabout, or to a somewhat higher temperature, during the making of the impregnating medium. I am aware of British patent to Abel, Number 1,962 of 1865, in which is described impregnating leather with mixtures of gums (including rubber) and waxes (including paraffin wax) the samehaving been heated to from 220 F. to 240 F-., c'are'being taken not to heat the mixture to over 260 F. Such an impregnating mixture is however, if containing 15% of rubber, of such high vis- 0. By heatingto over 150 0., the viscositycosity as to be practically useless for impregna'ting leather at 90 to 100 0. This same mixture however, when heated to 150 0., is of very much lower viscosity. As an illustration, 'a mixture of 15% rubber and 85% hard parafiin wax, heated to 260 F.

- (126.7 0.) had a viscosity at 95 0., of 7,000

seconds on the Story viscosimeter, while a precisely similar mixture (15:85) heated to 150 0., under preciselyfsimilar conditions, had a viscosity of about 480 seconds at'95 is somewhat further reduced. Other mixtures (i. e. mixtures of rubber and parafiin in-other proportions) heated to about 150 0., or a little below, having a viscosity not substantially above 500 seconds, are also very useful. Obviously the temperature should-not be carried to such a high point as to injure the waterproofing ualities of the mixture. The viscosity of t e mixture whether heated to 126.7 and 150 0., will be largely dependent upon the rubber content. It 1s obvious that t e permeating qualities of the mixture (at a given temperature) will increase with decreasing viscosityan'd vice versa. j v v The leather to be. impregnated can be soaked in the hot molten mixture, until sufficiently impregnated,this being done at say, 90 to 100 0., preferably 95 to 98 0., say at atmospheric ressure. I

In impregnating Ieather for shoe soles,

the leather can be soaked in the waterproofing mixture until suiiiciently impregnated, say for about 4'to 0 hours, a heavy belt leather may require 8 hours. This can be hastened by vacuum and pressure treatment, but is generally not needed. The impregnation is for many purposes, carried out as completely as possible, but in some cases a partial impregnation is sufficient.

The leather is preferably quite dry before immersing in the impregnating liquid. I may use air-dried'leather but it appears better to further dry the leather in a steam jacketed oyen, at say 98-100 0., just before s specific example of the compositlon to be employed for the impregnating bath the following are given:

E wiz-mple I 800 pounds of paraffin wax are melted and then heated at about 150 0., with 200 pounds of Para rubber, with stirring, until a uniform mlxture is obtained. Leather is then soaked therein, as above described, at

Example 2.

2,000 pounds of crude plantation rubber are mixed with 7,800 .pounds of paraflin wax and 200 pounds of ,gum thus added, at 150 0. to 155 0., which temperature is maintained 2 hours While stirring.

, Ewample 3;

. 8,500 pounds of parafiin wax, 1,000 pounds of vulcanized rubber scrap, and 500pounds of linseed oil are thoroughly stirred together, at 150 0., for three hours.

' While I have herein described a, good mode of reducing the viscosity and increasing the penetrating quality of the impregnating agent, this invention is not restricted to such method, but I consider the use of any like mixture of the substances herein described, having the low viscosity and high impregnating or permeating qualities, as withnr the scope of my invention, irrespective of how such properties are imparted between 5% and 50% of rubber with molten arafiin wax at about 150 0,, until a unifrom vdlatile solvents, and such mixture at 90 to 100 C. being of sufliciently low viscosity to readily and thoroughly penetrate thick leather, the amount of such 'molten state.

6. Leather impregnated with a. mixture paraffin wax and added substance being -suflicient to give the mixture a firm. waxy consistency at ordinary room temperature.

3. A method of waterproofing leather which comprises "impregnating the leather with a hot molten mixture containing from 10 to 50% of rubber in molten paraflin wax, together with a resinous substance and a drying oil, such mixture being free from volatile solvents and such mixture at 90 to 100C. being of sufiiciently low viscosity to readily and thoroughly penetrate thick leather, and the proportion of parafiin wax and resinous substance being suflicient to give the mixture a firm solid consistency atordinary room temperature.

4. A method of waterproofing leather which comprises thoroughly incorporating between 5% and 50% of rubber with molten arafiin wax at about 150 C., until a uniorm smooth mixture is obtained, which mixture, if-cooled to room temperature is a firm waxy solid, and incorporating other water-insoluble organic materialcapable of readily blending therewith, at any stage of the operation, and thereafter. impregnating the leather with said mixture, in the absence of volatile solvents, while such mixture is in a hot molten state.

5. A method of waterproofing leather which comprises thoroughly incorporating between 5% and 50% of rubber with molten arafiin wax at about 150 C., until a uniorm smooth mixture is obtained, which mixture, if cooled to room temperature is a firm waxy solid, and thereafter impregnating leather containing chromium compounds with said mixture, in the absence of volatile solvents, while such mixture is in a hot which is a firm waxy solid at normal temperature, such mixture containing about 7 8 to 85% of paraflin wax and about,l0 to 20% of rubber dissolved therein, such mixture having been heated to at least 150C to impart the desired penetrating properties thereto.

7. A method of waterproofing leather which comprises impregnating leather with a hot molten mixture containing about 78 to 85% of parafiin wax, and at least about 10% ofrubber dissolved therein, such mixture having been heated to about 150 (3., to impart the desired readily penetrating property thereto.

8. Flexible, substantially chrome-tannedleather impregnated wlth a mixture which is a relatively firm somewhat flexible solid at normal room temperature, but which is liquid when hot, such mixture comprising parafiin wax and from 5 to 50% of a water-proof rubbery gum dissolved therein, such mixture, when hot, having a readily penetrating quality and' a ow viscosity such as can be imparted thereto by' non-slippery heating a mixture of said substances to 9. Leather impregnated with a mixture which is a firm waxy solid at normal temperature, such mixture containing vabout 78 to 85% of paraffin wax and about 10 to 20% of rubber dissolved therein, such mixture having a low viscosity and a high penetrating power such as can be imparted by heat ing a mixture of said substances to at least 10. A method of waterproofing leather which comprises thoroughly incorporating between 5% and 50% of rubber with molten parafiin wax, such operation involving heating such substances to not below 150 6., but not-high enough to distill off the Wax or spoil the rubber until a uniform smooth vmixture is obtained, which mixture, if

cooled to room temperature is a firm waxy solid, and thereafter impregnating the leather with said mixture, in the absence of volatile solvents, while such mixture is in a hot molten state.

11. A process which comprises impregnating leather with a hot mixture which at normal room temperature is a firm waxy solid, and which at C. has a viscosity not substantially above 500 seconds gory), and which mixture contains para wax and a water-insoluble gum.

12. An impregnating and waterproofing agent suitable for impregnating leather which mixture at normal room temperature is a firm waxy solid, and which at 95 C. has a viscosity not substantially above 500 seconds (Story), and which mixture contains parafiin wax and rubber.

13. A,rubberarafiin mixture having viscosity at 95 not -above 480 seconds (Story) and containing' about 15% of rub-- ber A rubbe'r-paraflin mixture having a low a I viscosity when hot, corresponding to that obtained by heating a mixtureof said ingredi ents to at least 150 C.

15. A method of treating leather which comprises impregnating same with a mixture of parafiin wax and rubber, having a low viscosity and a high penetrating power such as can be imparted by heating such mixture to about 150 C.

16. Leather impregnated with a mixture of paraffin wax and rubber, having a low I viscosity and a high penetrating power such as can be imparted by heating such mixture to about 150 C 17. Chrome-tanned bark-retanned leather im regnated with a mixture of parafiin Wax an rubber, having a low viscosity and a high enetrating power such as can be imparte 150 C.

18. Chrome-tanned bark-retanned leather impregnated with a low viscosity 'mixture containing paraflin wax and rubber.

. 19. A chrome-tanned leather impregnated with a low viscosity mixture containing parafiin wax and rubber.-

In testimony by heatmg such mixture to about I HENRY NHAM.

whereof I aflix m signature.

V. Di 

